The central objectives of this research program on population and quantitative genetics are to characterize the nature and extent of genetic variation in populations, to study forces and their interplay that lead to the maintenance of this variation, and to make inferences about such forces from observations on populations. Research efforts are of a basic investigative nature and general in scope. They are directed at the construction of theoretical models, the development of the consequences of the models into verifiable predictions, and the development of methods of analysis of data to check the predictions. There is a concurrent accumulation and interpretative analysis of data obtained both by field observations and laboratory experimentation with natural populations. A major effort is directed at isoenzyme variation: extent and pattern of variation and covariation in natural populations, frequency compositions in experimental populations, basis of continuous variation in activity, response to environmental treatments and selection, and linkage and other disequilibria. Related studies are aimed at the development and experimental testing of useful numerical methods of classification. Analytical tools are being developed and evaluated in all phases of the research. Principally, experimental research is conducted with Drosophila and maize.